Metropolitan Police Commissioner Sir Bernard Hogan-Howe, said: "The patience and determination that Keith's widow, Elizabeth, has shown over the years as she has pushed for answers about her husband's murder has been inspirational. She so richly deserves those answers and justice.

"We accept the decision of the jury and our work to bring those responsible for Keith's murder to justice will not stop."

Crown Prosecution Service London prosecutor Jenny Hopkins said: "It was right that all the evidence in this case was put before a jury and we respect its decision."

Retired policeman Richard Coombes, 63, who survived the Broadwater Farm attack, said: "The jury has reached its decision and we must all respect that."

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Media captionRobert Hall looks at what happened on the night PC Blakelock died

PC Blakelock, 40, was repeatedly stabbed, and attempts made to decapitate him, as he tried to protect firefighters tackling a blaze at the height of the unrest on the Broadwater Farm estate on 6 October 1985.

During the trial, the jury heard Mr Jacobs had allegedly written a poem, while serving time in a juvenile detention centre, in which he boasted about "chopping" at the officer.

But his defence team claimed his account of the wounds the officer received did not match the post-mortem examination.

Mr Jacobs' prosecution followed an previous trial in 1987, when three men were convicted of the murder, before being freed four years later on appeal.

During the course of three separate investigations, a decision was made to give immunity to so-called "kickers" - those who were involved in the attack but did not use weapons - in exchange for their co-operation.

Among them were the prosecution witnesses given the pseudonyms Rhodes Levin and John Brown who both admitted kicking PC Blakelock and were given amnesty from prosecution.

Some of the witnesses also received payments from police for their co-operation, the court was told.

The judge said Mr Jacobs had been within his rights not to give evidence during his trial and the jury could draw their own conclusions about his decision not to take the witness stand.

Winston Silcott, one of the so-called Tottenham Three convicted of the murder of PC Blakelock in 1987, said outside the Old Bailey: "The police are bitter about what happened, that's why they brought this case.

"My conclusion is that they had promised the Blakelock family that they would get justice for him and so they were trying to get anyone they could.

"Vengeance, that's what the police were out to get. I just hope Nicky Jacobs will be able to rebuild his life after this."